1. Field of the Invention
This invention relates to the use of cationic polymers as soil release compounds in rinse aids for dishwashing machines.
Commercial rinse aids for dishwashing machines are mixtures of low-foaming fatty alcohol polyethylene/polypropylene glycol ethers, solubilizers (for example cumene sulfonate), organic acids (for example citric acid) and solvents (for example ethanol). The function of these rinse aids is to influence the surface tension of the water in such a way that the water is able to drain off the dishes in the form of a thin coherent film so that no droplets of water, streaks or films are left behind after the subsequent drying process. An overview of the composition of rinse aids and methods for testing their performance was published by W. Schirmer et al. in Tens. Surf. Det. 28, 313 (1991).
In machine dishwashing, it occasionally happens that firmly adhering soils such as, for example, oat flakes and starch deposits are not completely removed during the cleaning process.
2. Discussion of Related Art
It is known from EP-A-0 167 382, EP-A-0 342 997 and DE-OS 26 16 404 that cationic polymers can be added to dishwashing detergents to obtain streak-free cleaning of the surfaces.
EP-A-0 167 382 describes liquid detergent compositions which may contain cationic polymers as thickeners. Hydroxypropyl trimethyl ammonium guar, copolymers of aminoethyl methacrylate and acrylamide and copolymers of dimethyl diallyl ammonium chloride and acrylamide are described as particularly suitable cationic polymers.
EP-A-0 342 997 describes multipurpose cleaners which may contain cationic polymers, more particularly polymers containing imino groups.
DE-OS 26 16 404 describes glass cleaners containing cationic cellulose derivatives. The addition of the cationic cellulose derivatives improves drainage of the water so that no streaks are left behind on the cleaned glass.
EP-A-0 467 472 describes hard surface cleaners containing cationic homopolymers and/or copolymers as so-called soil release polymers. These polymers contain quaternized ammonium alkyl methacrylate groups as monomer units. These compounds are used to finish the surfaces in such a way that the soils are easier to remove the next time the surfaces are cleaned.
The documents cited above disclose the use of cationic polymers in cleaning formulations. There is nothing in any of these documents to indicate how it is possible in machine dishwashing to facilitate the removal of obstinate soils, for example starch-containing soils.
The problem addressed by the present invention was to provide a rinse aid which would enable firmly adhering soils, such as oat flakes and other starch deposits, to be readily removed from the dishes in subsequent cleaning cycles.